Change constructor visibility to global.

Constructors are always effectively global.

code/compiler/13/definition.cpp

@@ -83,7 +83,7 @@ void definition_data::insert_constructors() const {
 
         type_scheme_ptr full_scheme(new type_scheme(std::move(full_type)));
         full_scheme->forall.insert(full_scheme->forall.begin(), vars.begin(), vars.end());
-        env->bind(constructor->name, full_scheme);
+        env->bind(constructor->name, full_scheme, visibility::global);
     }
 }